Many scholars and scientists rely heavily upon digital data and content in their research.  Maintaining such digital resources over time is necessary to permit longitudinal or time lapse studies, and to preserve these researchers' ability to support, and others to evaluate, their findings.  Thus the need for “long-lived” collections of digital content and data.

Digital repositories are emerging to meet these needs. Some repositories specialize in data for particular fields or disciplines.  Others aggregate digital content on a variety of subjects.  A  number of assessment criteria are provided here to help libraries, scholars, publishers, and others judge the reliability of the repositories and digital preservation services they may choose to rely upon or support.  .